An experimental study of the long range behavior of the ground state X 1 Σ + g of Sr2 is performed by high resolution spectroscopy of asymptotic vibrational levels and the use of available photoassociation data. Ground state levels as high as v ′′ = 60 (outer turning point at 23Å and 0.1 cm −1 below the asymptote) could be observed by Fourier-transform spectroscopy of fluorescence progressions induced by single frequency laser excitation of the v ′ = 4, J ′ = 9 rovibrational level of the state 2 1 Σ + u . A precise value of the scattering length for the isotopologue 88 Sr2 is derived and transferred to all other isotopic combinations by mass scaling with the given potential. The derived potential together with already published information about the state 2 1 Σ + u directs to promising optical paths for producing cold molecules in the electronic ground state from an ultracold ensemble of Sr atoms.

Precise potentials for the ground-state X 1 ⌺ g + and the minimum region of the excited state 2 1 ⌺ u + of Sr 2 are derived by high-resolution Fourier-transform spectroscopy of fluorescence progressions from single-frequency laser excitation of Sr 2 produced in a heat pipe at 950°C. A change of the rotational assignment by four units compared to an earlier work ͓G. Gerber et al., J. Chem. Phys. 81, 1538 ͑1984͔͒ is needed for a consistent description leading to a significant shift of the potentials toward longer interatomic distances. The huge amount of ground-state data derived for the three different isotopomers 88 Sr 2 , 86 Sr 88 Sr, and 87 Sr 88 Sr ͑almost 60% of all excisting bound rovibrational ground-state levels for the isotopomer 88 Sr 2 ͒ fixes this assignment beyond a doubt. The presented ground-state potential is derived from the observed transitions for the radial region from 4 to 11 Å ͑9 cm −1 below the asymptote͒ and is extended to the long-range region by the use of theoretical dispersion coefficients together with already available photoassociation data. New estimations of the scattering lengths for the complete set of isotopic combinations are derived by mass scaling with the derived potential. The data set for the excited state 2 1 ⌺ u + was sufficient to derive a potential energy curve around the minimum.

We report on the first experimental observation of the ground electronic state of the LiRb molecule at high resolution. A large body of experimental data was collected which led to an accurate potential energy curve for this state. Transitions to the lowest triplet state were also observed, but these data are rather fragmentary and allow only a first attempt for the description of this state. Both potentials were used for evaluating published Feshbach resonances of this molecule. We compare the results of this study with those of the related LiK and LiCs molecules.

No abstract

Ventral ectodermal explants taken from early gastrula embryos of Xenopus laevis were artificially stretched either by two opposite concentrated forces or by a distributed force applied to the internal explant's layer. These modes of stretching reflect different mechanical situations taking place in the normal development. Two main types of kinematic response to the applied tensions were detected. First, by 15 min after the onset of concentrated stretching a substantial proportion of the explant's cells exhibited a concerted movement towards the closest point of the applied stretching force. We define this movement as tensotaxis. Later, under both concentrated and distributed stretching, most of the cell's trajectories became reoriented perpendicular to the stretching force, and the cells started to intercalate between each other, both horizontally and vertically. This was accompanied by extensive elongation of the outer ectodermal cells and reconstruction of cell-cell contacts. The intercalation movements led first to a considerable reduction in the stretch-induced tensions and then to the formation of peculiar bipolar "embryoid" shapes. The type and intensity of the morphomechanical responses did not depend upon the orientation of a stretching force in relation to the embryonic axes. We discuss the interactions of the passive and active components in tension-dependent cell movements and their relations to normal morphogenetic events.

We studied the molecule LiRb in the gas phase with high resolution by Fourier-transform spectroscopy of laser induced fluorescence. The spectra were assigned to transitions between the ground state X(1)Σ(+) and B(1)Π or D(1)Π states and showed perturbations. For levels with e symmetry the coupling to the nearby state C(1)Σ(+) was included in the analysis by means of coupled channel calculations. The evaluation gives potential energy curves for all three electronic states and the coupling functions for B-C coupling, which are related to the expectation value of the electronic orbital angular momentum operator L(+) or L(-). The same coupling between C and D states is considered, but is not yet as fixed as in the case B-C because of lack of data. The model was extended to include the Λ-doubling by distant electronic states through effective q-parameters, but their interpretation is incomplete because of several possible perturbing states and too few data.

The 2(2)Σ(+) and 4(2)Σ(+) excited states of (7)Li(40)Ca have been studied by high resolution Fourier-transform spectroscopy. The data on the lower state, 2(2)Σ(+), were obtained by analyzing the rotationally resolved spectra of the thermal emission of LiCa in the 2(2)Σ(+) → X(2)Σ(+) band around 9500 cm(-1). These data contained transitions mainly from v' = 0 and 1 for N' up to 92 and allowed us to derive molecular parameters describing the potential curve of the state close to its minimum. The dataset on the second state, 4(2)Σ(+), is much larger and comes from a laser-induced fluorescence experiment. The levels were excited by a single mode dye laser and the 4(2)Σ(+) → X(2)Σ(+) fluorescence was recorded through a Fourier-transform spectrometer. For both states potential energy curves and Dunham coefficients were derived and the spin-rotation structure was evaluated. The results are compared with theoretical and experimental data from the literature.

A high resolution study of the electronic states 1 1 Σ + u and 1 1 Πu which belong to the asymptote 4 1 D + 5 1 S and of the state 2(A) 1 Σ + u , which correlates to the asymptote 5 1 P + 5 1 S, is performed by Fourier-transform spectroscopy of fluorescence progressions induced by single frequency laser excitation. Precise descriptions of the potentials up to 2000 cm −1 above the bottom are derived and compared to currently available ab initio calculations. Especially for the state 1 1 Σ + u large deviations are found. Rather weak and local perturbations are observed for the states 1 1 Πu and 2 1 Σ + u , while a strong coupling of the state 1 1 Σ + u to the component Ω = 0 + u of the state 1 3 Πu, which belongs to the asymptote 5 3 P + 5 1 S, is indicated.